09/2023
To improve the temperature measurement not only visually, but also technically, I have installed an additional automation system. Previously, I had to swivel the measuring arm (which was made of plastic) over the turntable by hand (and turn it away again by hand at the end of the cutting process). I always had to pay close attention to the position of the IR temperature sensor, because the temperature sensor has a measuring cone, i.e. an area that is measured.
To improve the measurements, the arm should be positioned according to the size of the blank (12", 10", 7"). And because I generally hate monotonous, repetitive tasks (and am too lazy for them), I prefer to take the trouble to automate things.
So I thought I would control the Swivel arm with a servo motor. I first had to learn how to control a servo motor with Arduino, but that wasn't difficult.
It was more difficult to design the construction because I wanted the arm to be quiet, precise and durable. Therefore, friction surfaces such as aluminium on aluminium must be avoided. I therefore produced Teflon bushes at the friction points, which have low friction and are easy to machine. The cable routing through the whole part was a little more complicated, but I was able to manage that too.
The following two pictures show the construction of my moving element.
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I then fitted the servo motor to the moving disc drive and connected the two parts with a lever:
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I then fitted all the cover plates and started a first test run. It didn't immediately work as planned! I connected the 5V servo motor to the 5V "on-board power supply", which also supplies the Arduino microcontroller, the touch display and many other things. During the first test, all the displays started flashing and the relays clicked in an uncoordinated manner. The problem was that at the first moment the current consumption of the servo was so high that the voltage on one of the supply contacts collapsed. It was a bad contact there. And as I have a lot of plug contacts on my makeshift "grand-mother-board", troubleshooting was the first order of business. But after an extensive search, I was able to find and rectify the fault. I'll have to be even more careful with the crimp connections in future.
But it worked on the second attempt! As a test, I moved the arm back and forth twice at maximum speed. You can see this clearly in the following video.
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. VIDEO: MOVING ARM
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The first hurdle has now been overcome. But more needs to be done to ensure that it ultimately delivers good measurement results and controls the heating lamp properly.
So far, my control/regulation system has been quite simple:
- I set the desired temperature in the touch panel.
- The microcontroller took the setpoint and compared it with the actual value.
- If the turntable was rotating, then it continued (heating should not take place when the turntable is stationary, because then there is no even heating and the blank is deformed). In addition, my heating lamp is not centred for various reasons.
- If the actual value was too low (with a tolerance of one degree), the lamp was switched on via a relay.
- If the actual value was too high (with a tolerance of one degree), the lamp was switched off again via a relay.
But once a cutting thread formed on the plate (unfortunately this happens from time to time) and I had to remove it with a brush or cloth while cutting. I briefly created a shadow with my hand. What happened next was an interesting experience. The cooled area came to the measuring sensor and it said: "too cold". The lamp switched on immediately. With a warm-up time of around 0.5 seconds, it became really warm after 0.9 seconds.
And for all those who want to think along now: At 33.3 rpm, 0.9 seconds is half a revolution!
So it was the warm spot near the lamp and sensor and was warmed up even more. Of course, the sensor said "too hot" and the lamp switched off again. After a further 0.9 seconds (half a turn), the further cooled spot came to the measuring sensor (it was not heated). The game continued until one half to heat up and the other half continued to cool down, causing the blank to deform.
I'll explain how I managed to solve this problem in the next post.
Greetings from Austria
Thomas